1. Field of the Invention:
The present invention relates to an optical disk apparatus provided with means of determining whether or not a focusing pull has been conducted normally.
2. Description of the Related Art:
Recently, attention has been paid to optical information recording/reproducing apparatuses which by irradiating optical beams are capable of recording information on a recording medium at a high density and reproducing at high speed the information recorded on the recording medium at high density.
In such apparatuses, optical beams must be sufficiently stopped down when the information is recorded or reproduced because of the high density recording. For this reason, a focusing servo system is employed in which focusing of an objective lens for condensing the optical beams onto the recording medium is controlled so that recording or reproduction is performed in a focused state.
Such focus controlling techniques have been disclosed in the specification of, for example, Japanese Patent Laid-Open No. 63033/1984.
This technique utilizes the fact that the reproducing information signal is maximized in a state wherein the lens is focused, and involves focusing of the lens by the closing of a servo loop with the level of a focus error signal generated when the information reproducing signal is maximized serving as a desired value of the focusing servo system.
In this focusing control technique, the normal focusing state of the servo system is ensured if an optical system for irradiating optical beams of a light source onto the recording medium and leading light returning from the recording medium to a photo detector as well as the photo detector for outputting focus error signals are in a normal state. However, generally the optical system or the like is not always to be set in an optimum state. In such a case, the maximum level of an information reproducing signal does not coincide with the focused state. If the setting of the optical system or the like is outside a certain range of tolerance, the point at which the servo loop is closed deviates from the range in which a focusing pull is enabled, making it impossible for the optical system to be set in a focusing state. Even if the focusing pull is performed normally, if the position of the photo detector is shifted or if a subtracter for outputting focus error signals has an offset, the focused state of the servo system does not ensure an actual focused state, causing the beam to be condensed on the recording medium to be expanded and thereby reducing the reliability of recording/reproducing operations.
In consequence, the conventional optical information recording/reproducing apparatus of the above-described type has a disadvantage in that it does not offer a high level of reliability.